1. Field of the Invention
The invention relates to a brake system and a method of controlling the same brake system.
2. Description of the Related Art
An anti-skid (anti-lock) brake system (ABS) prevents a wheel from locking during hard braking and allows a steering operation during hard braking, and is a known as an active safety apparatus.
The following brake systems are known.                (1) A system in which an anti-lock control is changed in accordance with an index that indicates the momentum of a running vehicle (see Japanese Patent Application Laid-Open Publication No. 10-6968).        (2) A system in which a physical quantity that indicates the state of run of a vehicle is taken into account in determination of an ABS control strategy (see the specification of German Patent Application Laid-open Publication No. 19512766).        (3) A system in which the requested amount of control regarding an anti-lock control is set on the basis of the deviation of an actual yaw rate from a target yaw rate (Japanese Patent Application Laid-Open Publication No. 4-185562).        (4) A system in which a threshold of a target slip rate of an anti-lock control is controlled during an understeer/oversteer state of a vehicle (see Japanese Patent Application Laid-Open Publication No. 2-283555).        
However, in the related-art brake systems, the braking force may sometimes decrease depending on the road surface condition during the ABS control.